(1) Field of the Invention
This invention relates to alternative phase shifting masks for patterning a layer of negative photoresist to form a contact hole mask and to a method of using the alternative phase shifting masks to pattern a layer of negative photoresist to form a contact hole mask.
(2) Description of the Related Art
Conventional binary masks have been used to form contact hole masks in a layer of photoresist. As the contact holes become smaller phase shifting masks have been used to pattern the photoresist.
U.S. Pat. No. 5,498,579 to Borodovsky describes multiple exposures of a photosensitive layer to improve resolution in the patterning of the photosensitive layer.
U.S. Pat. No. 5,702,848 to Spence describes the use of phase shift masks using step regions that compensate for 0.degree. to 180.degree. transition effects.
U.S. Pat. No. 5,798,203 to Haraguchi et al. describes a method of forming a photoresist image using two exposures of the photoresist. The resist used in a positive resist and is exposed. The exposed resist is then changed in its character by baking the substrate in an amine gas to make an exposed portion insoluble in developer. An unexposed portion of the positive resist is then exposed a second time.